Oh dear, there is a glitch in the matrix (sound proof)

[Jimbo37]

Hi BuildHub'rs

I'm in the latter stages of a 2 story build with a joist and osb first floor. I have installed hushpanel 28 floating soundproof on top of osb, which seems very good. Problem is, my flue comes up internally from main living space through corner of master bedroom through 400x400mm hole with heat ventillation grill, bypassing the soundproof. All is not lost, as I can box in flue in upper floor. What product/ board should I use for good acoustic performance, please?